Broaching tools are well known. They are used for machining metal and particularly for forming slots in turbine wheel discs and the like. One such broaching assembly is disclosed in Keith A. Clapp et al., U.S. Pat. No. 4,243,347.
The broach assembly generally includes a plurality of disposable inserts precisely positioned within an elongated slot and clamped therein by means of side and front clamps. The contact surface of the side clamp forces the inserts against the side and bottom locating surfaces of the broaching tool. The front clamp is employed to force the cutting inserts longitudinally against corresponding stops.
Cutting inserts and the slots in which they are housed are machined within acceptable manufacturing tolerances. Accordingly, a gap may exist between one or more of the clamping surfaces and the clamping walls.
A gap between the cutting insert and corresponding clamping wall is detrimental because the cutting insert is subject to movement within the gap. If a cutting insert moves within the gap it can become misaligned. This can cause the cutting insert to fracture and/or wear unevenly. Since the quality of the overall tool is only as good as the worst cutting insert, the existence of a single damaged cutting insert may result in considerable downtime in replacing the damaged cutting insert or may even make it necessary to discard the entire broaching tool.
To overcome this problem, Clapp et al. employs a generally rectangular shim member disposed between the clamping surface and the cutting insert wall. The shim is formed of a soft metal such as brass or copper. The softness of the metal allows the shim to compensate for different sized gaps so that each cutting insert is placed flush against the corresponding clamping surface.
The use of soft metal shims, however, does not adequately solve the problem of cutting insert movement, which occurs for example, when the tool is subjected to unbalanced side loads. This is because the shim deforms when stressed and a gap can form betweeen the shim and the clamping surface and/or the cutting insert.
It is therefore an object of the present invention to provide a broach assembly in which the cutting inserts are uniformly clamped within the broach holder.
It is another object of the invention to provide a clamping system using circular wedges which are rotatable so that the clamping surfaces are aligned flush against respective cutting inserts and which prevents the formation of undesirable gaps.